Sections are just like gateway pages, except they provide a more logical breaking up of the site into sections. each section will appear in the top nav bar so will be accessible from every page of the site.

Sections can also have their own stylesheets which means they can have their own look and feel, making them feel much more like a different part of the site. 

In local government a good example of sections might be an About the council, section moving the democracy and policy making elements of the council into a separate section from the service delivery and giving people answers bits.